Optical driver circuitry for burst mode transfer

Abstract

An apparatus comprises a laser emitter configured to transmit laser energy across an air gap to a separate device, and a driver circuit electrically coupled to the laser emitter and to an electrical interface. The driver circuit is configured to detect voltage levels at the electrical interface including a first voltage level, a second voltage level, and a third voltage level, and drive the laser emitter at a first power level when detecting the first voltage level, drive the laser emitter at a second power level when detecting the second voltage level, and drive the laser emitter at a third power level intermediate the first and second power levels when detecting the third voltage level.

What is claimed is: 
     
       1. An apparatus comprising:
 a laser emitter configured to transmit laser energy across an air gap to a separate device; 
 a driver circuit electrically coupled to the laser emitter and to an electrical interface, wherein the driver circuit is configured to: 
 detect voltage levels at the electrical interface including a first voltage level, a second voltage level, and a third voltage level; and 
 drive the laser emitter at a first power level when detecting the first voltage level, drive the laser emitter at a second power level when detecting the second voltage level, and drive the laser emitter at a third power level intermediate the first and second power levels when detecting the third voltage level, wherein the electrical interface is an interface to a signal bus, and the first voltage level corresponds to a first logic level of the signal bus, the second voltage level corresponds to a second logic level of the signal bus, and the third voltage level corresponds to an idle state of the signal bus. 
 
     
     
       2. The apparatus of  claim 1 , wherein the electrical interface is a differential interface to a universal serial bus (USB). 
     
     
       3. The apparatus of  claim 1 , wherein the driver circuit is configured to drive the laser emitter with a first current level when detecting the first voltage, drive the laser emitter with a second current level when detecting the second voltage, and drive the laser emitter with a third current level when detecting the third voltage, wherein the third current level is intermediate the first and second current levels. 
     
     
       4. The apparatus of  claim 3 , wherein the driver circuit includes a first field effect transistor (FET), a second FET, and a third FET, wherein driver circuit is configured to: activate the first, second, and third FETs when detecting the first voltage level to sink the first current level from the laser emitter; activate only the first FET when detecting the second voltage level to sink the second current level from the laser emitter; and activate the first and second FETs when detecting the third voltage level to sink the third current level from the laser emitter. 
     
     
       5. The apparatus of  claim 1 , including: a photodiode configured to detect laser energy received across the air gap from the separate device, wherein the laser emitter and the photodiode are arranged on a single substrate. 
     
     
       6. The apparatus of  claim 5 , including a receiver circuit electrically coupled to the photodiode, wherein the receiver circuit includes a power monitor circuit configured to determine an average power of laser energy received across the air gap from the separate device, and generate an output voltage using a comparison of received laser energy to the determined average power of laser energy. 
     
     
       7. The apparatus of  claim 5 , including a processor circuit configured to communicate data with the separate device according to a USB protocol using the photodiode and laser emitter. 
     
     
       8. The apparatus of  claim 7 , wherein the processor circuit is configured to communicate data with the separate device according to a USB burst mode protocol using the photodiode and laser emitter, wherein the driver circuitry is configured to maintain the laser emitter at the third power level between bursts of data transmitted according to the USB burst mode protocol. 
     
     
       9. An apparatus comprising an optical interface, the optical interface including:
 an optical interface host side including a host-side laser emitter and host-side driver circuitry, wherein the host-side driver circuitry includes an electrical interface and is configured to detect voltage levels at the electrical interface including a first voltage level, a second voltage level, and a third voltage level; and drive the laser emitter at a first power level when detecting the first voltage level, drive the laser emitter at a second power level when detecting the second voltage level, and drive the laser emitter at a third power level intermediate the first and second power levels when detecting the third voltage level; and 
 an optical interface peripheral side separated from the optical interface host side by an air space, the optical interface peripheral side including a peripheral-side photodiode and peripheral-side receiver circuitry, wherein the peripheral-side receiver circuitry includes a power monitor circuit configured to determine an average power of laser energy received across the air gap from the separate device, and generate an output voltage using a comparison of received laser energy to the determined average power of laser energy. 
 
     
     
       10. The apparatus of  claim 9 , further including: a peripheral-side laser emitter; peripheral-side driver circuitry; a host-side photodiode; and host-side receiver circuitry; wherein the host-side photodiode and host-side laser emitter are arranged on a first substrate and the peripheral-side photodiode and peripheral-side laser emitter are arranged on a second substrate. 
     
     
       11. The apparatus of  claim 10 , including a host processor circuit electrically coupled to the optical interface host side, wherein the processor circuit is configured to initiate transmission of pulses of laser energy by the host-side laser emitter according to a duplex communication protocol. 
     
     
       12. The apparatus of  claim 9 , wherein the electrical interface of the host-side driver circuitry is an interface to a signal bus, and the first voltage level corresponds to a first logic level of the signal bus, the second voltage level corresponds to a second logic level of the signal bus, and the third voltage level corresponds to an idle state of the signal bus. 
     
     
       13. The apparatus of  claim 12 , wherein the electrical interface is a differential interface to a universal serial bus (USB). 
     
     
       14. The apparatus of  claim 9 , wherein the host-side driver circuitry is configured to drive the laser emitter with a first current level when detecting the first voltage, drive the laser emitter with a second current level when detecting the second voltage, and drive the laser emitter with a third current level when detecting the third voltage, wherein the third current level is intermediate the first and second current levels. 
     
     
       15. The apparatus of  claim 14 , wherein the host-side driver circuitry includes a first field effect transistor (FET), a second FET, and a third FET, and the driver circuitry is configured to: activate the first, second, and third FETs when detecting the first voltage level to sink the first current level from the laser emitter; activate only the first FET when detecting the second voltage level to sink the second current level from the laser emitter; and activate the first and second FETs when detecting the third voltage level to sink the third current level from the laser emitter. 
     
     
       16. A method of operating an optical interface, the method comprising:
 detecting voltage levels at an electrical bus interface of a first device, the voltage levels including a first voltage level, a second voltage level, and a third voltage level; 
 wherein the first voltage level corresponds to a first logic level of the signal bus, the second voltage level corresponds to a second logic level of the signal bus, and the third voltage level corresponds to an idle state of the signal bus; and 
 transmitting laser energy using an optical interface of the first device across an air gap to a second device, wherein the transmitting includes driving a laser emitter at a first power level when detecting the first voltage level, driving the laser emitter at a second power level when detecting the second voltage level, and driving the laser emitter at a third power level intermediate the first and second power levels when detecting the third voltage level. 
 
     
     
       17. The method of  claim 16 , including:
 detecting transmitted laser energy at the second device; 
 determining average power level of the detected laser energy; 
 determining a logic level of subsequently detected laser energy by comparing a power level of the subsequently detected laser energy to the determined average power; and 
 generating an output voltage at the second device according to the determined logic level. 
 
     
     
       18. The method of  claim 16 , wherein detecting voltage levels includes detecting differential voltage levels at a universal serial bus (USB) interface of the first device. 
     
     
       19. The method of  claim 18 , wherein the transmitting the laser energy includes transmitting the laser energy according to a USB protocol burst mode.